The invention relates generally to knife blades and deals more particularly with the construction of and the method for making knife blades for cutting sheet material which blades exhibit some self sharpening characteristics.
A blade of the general type with which this invention is concerned is shown in U.S. Pat. No. 3,681,846 to Gerber. The '846 blade has three layers, a relatively hard layer sandwiched between two relatively soft layers. In one embodiment of the '846 blade, the inner layer is made of tungsten carbide and the two outer layers are made of steel or aluminum. An outer face of each outer layer is bevelled, and ideally, the two bevelled faces converge upon an exposed edge of the inner, relatively hard layer such that the exposed edge of the inner layer protrudes slightly from the outer layers forming a cutting edge or peak to the knife blade. The outer layers support the inner layer. In this embodiment, the thickness of the relatively hard inner layer varies in the longitudinal direction of the cutting edge so that the cutting edge wears unevenly forming a serration. Eventually, the cutting edge dulls and may be sharpened by one or two grinding wheels which bear against both of the outer, relatively soft layers of the blade.
It has proven difficult to accurately grind the two outer faces of the relatively soft layers such that the peak of the blade is formed exclusively by the exposed edge of the inner layer. The reason is that it is difficult to align the grinding wheel such that its axis is precisely parallel to the plane defined by the inner layer and misalignments of only a few thousandths of an inch result in the peak of the blade being partially formed by the outer, relatively soft layers, in which cases, the blade dulls easily.
Accordingly, a general object of the invention is to provide a knife blade for cutting sheet material which blade does not dull easily.
A more specific object of the invention is to provide a blade of the foregoing type which does not require precise sharpening.
Another specific object of the invention is to provide a knife blade of the foregoing type which exhibits some self-sharpening properties.
Another general object of the invention is to provide methods for making the cutting blades of the foregoing type.
Other objects of the present invention will become apparent from the following detailed description.